The outside offset in your image above isn’t correct either - IMO, it should look like this (sharp corners):
(try it with round corners and you will see it works better)
The offset code for Breps is also not robust - especially with sharp corners - if you try any complex polysurface in Rhino with OffsetSrf or Shell, you will see.
agreed to that i tried to model simple rectangular underpass under railtrack. offsetsrf polysurface of innerwalls and it failed. i compared to microstation with the same geometry and there was no problem. i posted it here, others said parasolid is much better (more expensive) but i am asking where should development go with rhino. its version 7 and these are basic geometric operations which should have been resolved since earlier versions. thats why i think there would be room for rhino next similarly to vray next. no evolution but revolution
I can reassure you that you are not the only one feeling this.
Just for fun, as I was running some toolpaths this afternoon - here is RhinoCAM’s outside profiling offset with a 6mm cutter (the ‘slot’ is 5mm wide)…
Here is the inside offset with a 16mm tool (the inner space in the lower left corner is 15mm wide):
I wanted to try this but I get an error “NoneType is not supported” when I try to plug in my bad “native” example into it and I do not know why.
Anyone know if offset curve is being improved for Grasshopper 2?
Yes, wow thank you! 
You know, sometimes I am baffled by how Grasshopper doesn’t even have the most basic (convenience) functionality, and sometimes turns out it has, so it’s difficult to know what to expect when for me (still feeling as a beginner) it’s all over the place (and I admit I’m all over the place too). 
